We are investigating how cells interact in a harmonious way over long distances via a diffusible chemotactic agent and by direct cell-cell contacts. The model system studied is D. discoideum. These amoebae will, under defined conditions, migrate chemotactically toward central collection points where they establish the intercellular connections basic to the formation of a multicellular organism. Our immediate approach to understanding how these cells process sensory information leading to a locomotory response is to study the regulation of the plasma membrane receptor for the chemoattractant of these cells, cAMP. In the current year, we have attempted to identify the molecular entity involved in chemoreception.